Edge isolation of photographic imagery



March 23,` 1-965 A. B. CLARKE EDGE ISOLATION OF' PHOTOGRAPHIC IMAGERY Filed June 25, 1962 lli" "United States Patent Ollice 3,174,851? Patented Mar. 23, 1965 3,174,857 EDGE ISLAUSN UF PHTGRAPIEC EMAGERY Alva B. Clarke, Arlington, Va., assigner to the United States of America as represented by the Secretary ci the Interior Filed .lune 25, 1961?., Ser. No. 2%,136

Claims. (Cl. ila-27) The invention herein described and claimed may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of royalties thereon or therefor.

The present invention relates to improvements in photographic techniques. A method is disclosed for producing a photographic negative wherein continuous tonal variations intermediate the darker or denser, and the lighter areas, have been diminished extensively, such that a positive made from this negative would be seen to contm'n only areas of uniform densities. rl'his nearly total elimination of areas of gradual differences in shading between the dark and light areas on the photograph made in this manner, achieves a diagrammatic representation wherein the forms of the dark areas symbolically define the ohiects to which they correspond.

Particular utility for the present invention is found in the art of photogrammetry as it involves the processing, compilation, and analyzation ot aerial photographs used in connection with producing topographic maps. For this purpose it is desirable that the varying densities of an aerial photograph be compressed while preserving, and in many cases increasing the contrast of line detail in the contents ot the photograph. This enhancing of the more significant details and subduing of the less significant, provides an appreciable aid in the selection and interpretation processes required for topographic mapping. Imagery of t:

maximum significance to the map compiler or photointerpreter almost universally involves man-made, or manmodied objects, or natural surface features such as vegetation and drainage. All these features are characterized by relatively continuous edges. The presence in a photograph of any unbroken line or edge, especially if straight or of simple curves, almost always indicates the presence of man-made or man-modified objects warranting display as planimetrie features. Continuous but less simple curved lines more commonly indicate drainage patterns, andclosed continuous lines or edges often indicate vegetation patterns. The important common characteristic of all this photographic evidence is the presence of edges.

Therefore, to 'attain the desirable end of enhancing detail of maximum significance while suhduing details of lesser importance, it should be necessary only to emphasize all edges where they appear in the aerial photograph. rThat edge emphasis does greatly assist the map compiler in interpreting detail from photographs is already common knowledge, yand many diiiicult and tedious techniques and much complex Aand expensive equipment have been used by map interpreters to obtain various degrees of edge enhancement. Photographic processes used for edge emphasis include the Eastman Kodak Tone-Line and Army Map Service Photoline unsharp masking techniques, a full disclosure of which is found in the article The Use of Photography To Achieve Basic 1Principles of Map Design, by John St. Clair and Mylon Merriam, Photogrammetric Engineering, lune 1960, pages 498 to 504, and in Patent No. 2,407,211 issued to l. A. C. Yule on September 3, 1946. Techniques described in this article and patent require that there be an exact registration of all points of two photographic copies in each step and involve other precise and time-consuming laboratory procedures. Hence, it is difficult by means of these processes to retain small obiect edges, and their applicability on a production basis is evidently not practicable. Electronic edgeenhancement systems developed for intelligence use are inherently complex and expensive, lack adequate resolution, and contain fundamental distortions that make them unadaptable to the precision requirements of topographic mapping.

The simple, inexpensive method of the present invention yaccomplishes an edge isolation elect to a greater or lesser degree for all edges as they appear in the aerial negative and in precisely the same location. Further, it is adaptable to negatives of extreme density which are beyond the normal range of automatic printers. Basic to this method is the phenomenon of photoluminescence, which is the property of certain substances to absorb radiation of one wavelength and emit radiation of another wavelength. Application of this phenomenon to the invention takes the form of a zinc sullide phosphor coating on a sheet of glass, which is adapted to be exposed to the radiations of ultraviolet and infrared lamps simultaneously. Absorption by the coating of the ultraviolet radiation, causes the phosphor to be photoluminescent by reason of its phosphorescence properties. However, the phosphor coating is also inversely sensitive to red and infrared wavelengths, so that exposure of the coating to the latter is elective to suppress the luminescence due to the absorption ot the ultraviolet. Consequently, a photographic negative positioned in the path of infrared radiation may be employed to determine the distribution of such radiation transmitted to a phosphor coating, providing thereby Ka control upon the distribution of the photoluminescence emanating from the coating when exposed to ultraviolet radiation. Exposure of a photosensitive material to the controlled emanated luminescence would na trally cause this material to retain thereon lan image of the light distribution.

An object of the present invention is therefore to provide a method of reproducing photographic images to consist of light and dark areas having substantially only one degree of contrast relative to each other.

Another object of the invention is to provide a method for producing a View having the characteristics of a graphic illustration consisting of distinct lines and forms, from a pictorial view comprising parts having the usual range of varying densities.

The manner in which the instant invention is performed will be fully understood from the following description when read in connection with the accompanying drawings in which:

FIG. l is a schematic showing of one possible structural arrangement for ellectuating the method of the invention;

FlG. 2 is an explanatory diagram illustrating the principle upon which the operation of the arrangement of FlG. l is based; and

FIGS. 3a and 3b are idealized views of a normal aerial photograph, and the image of this photograph produced by the method according to the present invention, respectively.

To facilitate the practice `oi the invention, application is made of the physical principles previously explained, in a scheme comprising light producing and controlling elements arranged as shown in FIG. l. Within a light proof enclosure 1, comprising a base part 4, and a cover part 6, joined by a suitable hinged construction, a supporting frame 8 is mounted in an opening through the upper surface of the base part 4. Fitted and fastened within frame S are a relatively thick glass plate 12, the upper surface of which is coated with a .002 phosphor screen la, of ZnS, Cu, and an ultraviolet tilter 16 coated with .003" of suitable gelatin which is covered over with a .0015 inch protective sheet, the purposes of which are to be hereinafter explained. Below glass plate l2, a source ot ultraviolet light such as a iluorescent lamp 18 emitting light at from about 3300 to 4050 Angstrorn units, is attached to a lower inner surface of the base part 4. The glass enveloping this ultraviolet lamp functions as a filter equivalent to Corning No. 5940 which transmits 80 percent of the radiation at 3650 Angstrorn units and a negligible amount at 4000 Angstrom units. Lamp 18 is in position to radiate its ultraviolet light through the glass plate l2, for absorbtion by the phosphor screen 14. Afiixed to the inner surface within cover part 6, is an electrical fixture comprising several incandescent lamps 20, constituting a source of infrared light, backed up by a conventional reflector means 22. Secured within the upper part d, so as to be positioned to overlie the elements in frame S, when the enclosure l is closed, is a frame-like bracket 24 having assembled within it a photographic negative transparency 26, a sheet of photosensitive material 28, and an infrared filter 30. Infrared filter 30 is situated in the path of the light emitted from the lamps 20, for limiting the effective light transmitted, to infrared above the visible range at approximately l0,000 to 20,000V Angstrom units. Arranged thusly, negative 26 is located with its emulsion side up, in juxtaposition to and between the filtered phosphor screen 14, 16, and the sensitized paper 2S, the latter being in the nature of a high contrast, orthochromatic stablebase film having a sensitivity of 2,500 to 6,000 Angstrorn units. Since the thickness of the base of negative transparency 26 ranges from .004 to .007 inch, the total distance between the effective surface of the transparency and phosphor screen 14, ranges from about .0085 inch to not more than .0115 inch. Some of the factors which may be considered to affect this total distance are the granularity of the phosphorescent screen, theV average degree .of sharpness of the control transparency, as well as the particular photographic materials available for use in the instant method. Although the average size of the granules of zinc sulfide is estimated to be approximately 0.0004 inch, clumping and gathering together of the granules forms a much larger effective dimension. Therefore, the most efficient part of the phosphor screen is at the edges of cracks between adjacent clumps, and as a general rule the areas of most eicient phosphorescence are separated by no more than 0.010 inch. This distance would normally be a limiting factor for the nearness to which the negative photographic image could be placed in respect to the phosphor screen without excessive granularity of the photographic image produced. However, should the edges'of the negative transparency images lack sharpness or exhibit a gradual transcency fro-m the darker to the lighter densities, the desired edge Veect could be lost by having the negative film in too close proximity to the phosphor screen. It would then be necessary to extend the separating distance by such means as a thin glass plate, to preserve the image outline.

When the FiG. 1 arrangement is made operative by conventional electrical switches, timer, and related circuit means, ultraviolet source 18 radiates a range of ultraviolet with a peak emission of 3,650 Angstrom units, exciting the phosphor screen 14, which luminesces with an emission range of 4,000 to 5,900 Angstrorn units. Since filter 16 absorbs the ultraviolet rays shorter than 4,000 Angstrom units visible light is transmitted from the filtered phosphor screen le. Light rays from the incandescent lamps received through the filter 30, are transmitted as infrared above the visible range to pass to the phosphor screen 14, after having their intensity and distribution determined by the opacity of the negative 26. As a result, luminescence from the phosphor screen ld is quenched inversely proportional to the density of the negative 26, converting the phosphor screen thereby, to a point-to-point image modulated light source. This light positive produced on the phosphor screen, is consequently effective to expose the photographic emulsion on the sensitized material 28.

A detailed description of a procedure similar to that already described, may be found in an article The Fluoro-Dodge Method for Contrast Control by Alfred I. Watson, in Photogrammctric Engineering, September 1958, pages 638 to 643. The paper print produced in accordance with the method disclosed by this article, makes availablea dodged photograph having its high density areas noticeably lightened. As a result, much of the pictorial detail covered over within the dense areas are made prominent since the diminution of the photographs over-all density allows the revelation of hidden outlines otherwise lost by their lack of any contrast in the high density areas. Thus the ideal dispositive or Contact print made from an original film in this manner, contains all significant imagery in the middle density range. Such dodging methods are applied in diapositive and Contact printing to compress the wide range of densities on the original film into the optimum range on the diapositive or print. However, the procedures of the present invention extend such teachings by recognizing and effectively utilizing a further related but very different phenomenon. This further phenomenon advantageously employs certain diffusion effects of infrared and luminescent light produced in connection with the present procedures around a dense area on a negative. A dense area of this nature is represented in FIG. 2 by the shaded portion 37 on the negative 26. Also shown in this gure are a dashed line 35 indicative of filtered infrared light directed at the edge 36 of the shaded area 3?, and a dashed line 33 indicative of diffused light scattered around this edge. Phosphor screen lll receives the light 35 at a point 39, and the light 38 reaches the screen at a point d0, beneath a portion of the dense area 317, adjacent the edge 36. Accordingly, light 35 and the light radiated to the left thereof in FiG. 2, strikes the phosphor screen lil, and quenches the available luminescence from the screen, to the left of point 3@ which is designated area A in the figure. Difused infrared light striking the phosphor screen between points 39 and fifi designated area B in the figure, is also disposed to quench the screens luminescence, but since diffused infrared is of diminished intensity, its quenching action is far less effective and a siginificant measure of luminescence continues in this area. Aligned beneath and shielded by the cover of the negatives dense portion 37, is a section of the screen 14 to the right of point 40, designated in FIG. 2, as area C, which luminesces fully. Such luminesces fully. Such luminescence though does not reach the sensitized material 2S through the intervening dense area 37. However, luminescence radiating from such areas on the phosphor screen represented by area B, is 0f sufficient intensity to scatter around a demarking line such as edge 36, and to expose a band of emulsion 42 on the sensitized material 2S. Since those portions of the material 23 aligned over areas A and C are not exposed to luminescence to any extent, the band 42 outlines on the sensitized material a form corresponding to the dense area on the negative. The sensitized material ZS thereby receives thereon a diagrammatic duplication of the configuration on the negative 26. A significant degree of density compression and definition of detail are invariably obtained in this manner since the areas of least or most transmission of light to the sensitized material occur at the edges of the dense areas.

More specifically, the edge isolation as accomplished according to the method of the present invention, results in the edge of the dense area being compressed to form a distinctive outline, and any tonal quality in the light and dark areas outlined, is substantially eliminated. As an initial step in this method, a photographic negative of the pictorial representation to be processed, is made part of the arrangement shown in FIG. 1. The distance between this negative and the phosphor screen 14 is a factor in determining the nite width of the edge isolated lines formed. Narrower boundary lines are obtained by shortening this distance within such limits previously indicated. Equipment such as described for the Fluoro-Dodge time depends on such factors as the age and efficiency of the lamps 18 and 20, the energy state of the screen 14, and the density of the negative transparency 26. Allowing for optimum structural and operational conditions, and considering the screen 14 to be initially in a ground or dead state with no energy output, the exposure time should be approximately 15 seconds. The exposed film positive is developed in a moderately contrasty developer, such as Kodak D-19, following the recommended procedure. Abrupt density changes in this positive appear as clear lines in juxtaposition to lines of extreme density. When dried, this film positive becomes a master from which new negatives are made such as by direct contact printing. In the event that a modification in scale is desircd for the transparency, the original negative may be projected through an appropriate lens system upon a sensitized surface whereby the scale of the positive made thereby is changed as required. By contact printing the desired scaled negative is then made.

For the second stepin the method of the invention, a iinal negative is made from the transparency of the first step, using an arrangement such as shown in FIG. l, with similar high-contrast orthochromatic stable-base film, and exposure with mam'mum infrared. In addition to an active basic exposure time of about 40 seconds, a delay of approximately one minute before removing the iilrn, permits rnore exposure in the dense areas of the positive transparency by utilizing the persistence or afterglow of the phosphor screen. This second step provides a way of accentuating already enhanced edges and at the same time further subduing less important imagery. In the positive rnade by the first step, there are dark lines along the image borders which have a density higher than that of the surrounding background. Clear lines adjacent to these dark lines allow additional passage of infrared on the second step and thus further accentuate the representations of dark lines in the negative of the second step. This final negative is developed in high contrast developer of the type used for line and half tone work. if subdued tonal detail is desired, the negative may be developed in diluted Eastman Kodak Dektol or equivalent. The final negative is an accurate representation of all the image borders in the original negative. Other selections of film and developer combinations allows for a control of the degree of edge emphasis to be achieved by this method. For complete isolation or total elimination of tone, the film is processed in a caustic developer, such as Kodalith. In the negative produced thereby, the background becomes opaque, and only clear lines are left to represent the original image edges.

As indicated previously, various lms and developers may be used to regulate the contrast between the demarcation lines and the intervening neutral tones, as well as to accommodate extreme contrasts in original negatives and to facilitate press plate making Without half-tone screening. To the end that a negative produced by the method, may be printed on a Zinc or aluminum plate for offset printing or by some other means photo-mechanically reproduced, it is necessary to either render the intermediate tones as small dots or narrow continuous lines. In the latter case the iinal negative produced has to be of sutiicient density in the background areas to prevent exposure in that area. Exemplary combinations of film and developer, are listed below in the orders of the lowest contrast levels to the highest practical limits.

Developer 1 Film For use in first For use in second step step Highlight Masking D-n Dektol. Photomeehanlcal.

v PhotomeehaiiieallEastman Kodak trade name designations are used for convenience, and other equivalent developers would be suitable.

Manifold beneficial uses of the method of the invention are readily apparent. Aerial photographs processed by the method are transformed into map-like representations wherein natural and man-made objects appear to have characteristic symbolic forms. The method therefore provides a semiautomatic procedure for representing prominent terrain features by image symbols which in many respects are superior to graphically constructed symbols manually located on topographical maps. Depicted in FIG. 3a isa schematic representation of an areial photograph wherein variations in the Weight and density of shade lines are intended to be indicative of variations in the tonal qualities of shaded areas on the photograph. The rural scene shown in FIG. 3a comprises natural objects such as clumped trees 51, at the base of a hill 52, an orchard 53, including young trees 54, bordered by larger trees 5S, a stream 56, a gully 57, a depression 58 such as might be caused by an excavation, and flat pasture S9. Man-made objects are also shown and include roads 60, a culvert 61, a building 62, and an asphalt driveway 63. Practice of the method of the invention using the negative 0 of the 1FIG. 3a photograph, produces the edge isolated photograph schematically represented in FIG. 3b. Each of the objects S1 to 63 noted in FIG. 3a, is also to be seen in FIG. 3b, but with additional emphasis as to its form and character. The variations in tonal quality are eliminated, and the outlines remaining are basically uniform to the extent where they may be considered symbolic. It is evident that when made from orthophotographs of the type described in Patent 2,869,419, issued January 20, 1959, to R. K. Bean, the imagery of edge isolated photographs is accurately positioned and the resulting product is a very useful planimetrie map. Of course, the production of special purpose maps for which standard cartographie symbolization is not necessary is greatly facilitated by the method of the present invention.

Edge represented maps may be economically duplicated since they do not require half tone screening for their reproduction by lithography, and may be presented in publications by the less expensive offset process. Further uses of this method are found in producing photographs of particular areas whereon patterns valuable to geologists and others interested in the general configuration of the terrain, are often more easily detected in edge-isolated prints than in the original photograph. The use of edge isolated photographs in stereoscopic viewing improves the resultant image since contrast may be greatly diminished in such photographs.

Reasonable variations and modifications are possible within the scope of the foregoing disclosure and the appended claims to the invention.

What is claimed is:

l. in a method for reproducing the image of a normal negative transparency to form an edge isolated image on a final negative transparency, the steps of initially arranging in a stacking order the normal negative transparency, a sheet having a photographically sensitive emulsion surface nonsensitive to infrared radiation being transmitted therethrough, a filter passing infrared radiation above the visible range, and a source of infrared radiation,

further arranging in close juxtaposition to the underside of the normal negative transparency and in a stacking order therefrom, a filter absorbing ultraviolet radiation shorter than 4000 Angstrom units and transmitting visible light, a sheet of phosphor material, and a source of ultraviolet radiations, said phosphor material being activated by application thereto of the ultraviolet radiations whereby it luminesces and produces light, said light being subject to quenching by ltered infrared radiations passing through the sheet having an emulsion surface, the normal negative transparency, the ultraviolet lter and received on the phosphor material,

exposing the said emulsion surface to a pattern of luminescent light produced from the phosphor material resulting from the interaction thereon of the ultraviolet radiations, and the ltered infrared radiations received thereon whereby a positive latent image is formed on said sheet having the sensitive emulsion surface,

developing said positive,

rearranging the initial stack to include in place of the sheet therein, a similar sheet having a photographically sensitive emulsion surface nonsensitive to infrared radiation being transmitted therethrough, and in place of the normal negative transparency, the developed positive,

exposing the said similar sheet having an emulsion surface to a pattern of luminescent light produced from the phosphor material resulting from the interaction thereon of ltered ultraviolet radiations and the filtered infrared radiations passing through said developed positive whereby a negative of the said de- S Vveloped positive is created on the said similar sheet having the sensitive emulsion surface, and developing said last mentioned negative to achieve the inal negative transparency having thereon the edge isolated image.

2. in the method of claim 1, wherein the quenching infrared radiations are maintained for a time to produce a maximum effect in said steps creating the positive and the iinal negative.

3. In the method of claim 1, wherein the development of the said nal negative is processed in a caustic high contrast developer.

4. In the method of claim 1, wherein the positive of the said negative transparency created from the said sheet having the sensitive emulsion surface, is a transparency.

References Cited by the Examiner UNITED STATES PATENTS 1,966,322 7/34 Tuttle 96-27 2,988,978 6/61 Craig 96-27 3,085,154 4/63 Kelsh 96-27 FOREIGN PATENTS 810,526 3/59 Great Britain.

OTHER REFERENCES Clerc: Photography, Theory and Practice, 2nd ed., 1930, pub. by Sir Isaac Pitman & Sons, Ltd., pp. 242 and 369.

NORMAN G. TORCHLN, Primary Examiner.

HAROLD N. BURSTEDJ, Examiner. 

1. IN A METHOD FOR REPORDUCING THE IMAGE OF A NORMAL NEGATIVE TRANSPARENCY TO FORM AN EDGE ISOLATED IMAGE ON A FINAL NEGATIVE TRANSPARENCY, THE STEPS OF INITIALLY ARRANGING IN A STACKING ORDER THE NORMAL NEGATIVE TRANSPARENCY, A SHEET HAVING A PHOTOGRAPHICALLY SENSITIVE EMULSION SURFACE NONSENSITIVE TO INFRARED RADIATION BEING TRANSMITTED THERETHROUGH, A FILTER PASSING INFRARED RADIATION ABOVE THE VISIBLE RANGE, AND A SOURCE OF INFRARED RADIATION, FURTHER ARRANGING IN CLOSE JUXTAPOSITION TO THE UNERSIDE OF THE NORMAL NEGATIVE TRANSPARENCY AND IN A STACKING ORDER THEREFROM, A FILTER ABSORBING ULTRAVIOLET RADIATION SHORTER THAN 4000 ANGSTROM UNITS AND TRANSMITTING VISIBLE LIGHT, A SHEET OF PHOSPHOR MATERIAL, AND A SOURCE OF ULTRAVIOLET RADIATIONS, SAID PHOSPHOR MATERIAL BEING ACTIVATED BY APPLICATION THERETO OF THE ULTRAVIOLET RADIATIONS WHEREBY IT LUMINESCES AND PRODUCES LIGHT, SAID LIGHT BEING SUBJECT TO QUENCHING BY FILTERED INFRARED RADIATIONS PASSING THROUGH THE SHEET HAVING AN EMULSION SURFACE, THE NORMAL NEGATIVE TRANSPARENCY, THE ULTRAVIOLET FILTER AND RECEIVED ON THE PHOSPHOR MATERIAL, EXPOSING THE SAID EMULSION SURFACE TO A PATTERN OF LUMINESCENT LIGHT PRODUCED FROM THE PHOSPHOR MATERIAL RESULTING FROM THE INTERACTION THEREON OF THE ULTRAVIOLET RADIATIONS, AND THE FILTERED INFRARED RADIATIONS RECEIVED THEREON WHEREBY A POSITIVE LATENT IMAGE IS FORMED ON SAID SHEET HAVING THE SENSITIVE EMULSION SURFACE, DEVELOPING SAID POSITIVE, REARRANGING THE INITIAL STACK TO INCLUDE IN PLACE OF THE SHEET HTERIN, A SIMILAR SHEET HAVING A PHOTOGRAPHICALLY SENSITIVE EMULSION SURFACE NONSENSITIVE TO INFRARED RADIATION BEING TRANSMITTED THERETHROUGH, AND IN PLACE OF THE NORMAL NEGATIVE TRANSPARENCY, THE DEVELOPED POSITIVE, EXPOSING THE SAID SIMILAR SHEET HAVING AN EMULSION SURFACE TO A PATTERN OF LUMINESCENT LIGHT PRODUCED FROM THE PHOSPHOR MATERIAL RESULTING FROM THE INTERACTION THEREON OF FILTERED ULTRAVIOLET RADIATIONS AND THE FILTERED INFRARED RADIATIONS PASSING THROUGH SAID DEVELOPED POSITIVE WHEREBY A NEGATIVE OF THE SAID DEVELOPED POSITIVE IS CREATED ON THE SAID SIMILAR SHEET HAVING THE SENSITIVE EMULSION SURFACE, AND DEVELOPING SAID LAST MENTIONED NEGATIVE TO ACHIEVE THE FINAL NEGATIVE TRANSPARENCY HAVING THEREON THE EDGE ISOLATED IMAGE. 